FIG. 1A shows a cross-sectional view of a wellbore 10 having a casing 20 positioned through a formation. Typically, the casing 20 is set with concrete to strengthen the walls of the wellbore 10. Once the casing 20 is set, various completion operations are performed so that oil and gas can be produced from the surrounding formation and retrieved at the surface of the well. In the completion operations, completion equipment, such as perforating guns, setting tool, and pressure isolation plugs, are deployed in the wellbore 10 using a wireline or slick line.
The wellbore 10 is shown in a stage of completion after perforating guns have formed perforations 13, 15 near production zones 12, 14 of the formation. At the stage shown, a pressure isolation plug 100 on the end of a wireline 40 has been deployed downhole to a desired depth for isolating pressures in the wellbore 10. The plug 100, which is shown in partial cross-section in FIG. 1B, has a mandrel 110 and a packing element 120 disposed between retainers 150A-B and slips 130A-B. The overall outside diameter D of the plug 100 can be about 3.665-inches for deployment within casing 20 having an inside diameter of about 3.920 or 4.090-inches.
After being deployed in the casing 20, a setting tool sets the tool by applying axial forces to the upper slip 130A while maintaining the mandrel 110 and the lower slip 130B in a fixed position. The force drives the slips 130A-B up cones 140A-B so that the slips 130A-B engage the inner walls of the casing 20. In addition, the force compresses the packing element 120 and forces it to seal against the inner wall of the casing 20. In this manner, the compressed packing element 120 seals fluid communication in the annular gap between the plug 100 and the interior wall of the casing 20, thereby facilitating pressure isolation.
Once set in the desired position within the wellbore 10, the plug 100 can function as a bridge plug and a frac plug. For example, the plug 100 has a lower ball 180 and a lower ball seat 118 that allow the plug 100 to function as a bridge plug. In the absence of upward flow, the lower ball 180 is retained within the plug 100 by retainer pin 119. When there is upward flow, however, the lower ball 180 engages the lower ball seat 118, thereby restricting flow through the plug 100 and isolating pressure from below. During completion or production operations, for example, the plug 100 acting as a bridge plug can sustain pressure from below the plug 100 and prevent the upward flow of production fluid in the wellbore 10.
To function as a frac plug, for example, the plug 100 has an upper ball 160 and an upper ball seat 116 in the plug. In the absence of downward flow, the upper ball 160 is retained within the plug by retainer pin 117. When there is downward flow of fluid, however, the upper ball 160 engages the upper ball seat 116, thereby restricting flow of fluid through the plug and isolating pressure from above. In a fracing operation, for example, operators can pump frac fluid from the surface into the wellbore 10. Acting as a frac plug, the plug 100 can sustain the hyrdualic pressure above the plug 100 so that the frac fluid will interact with the upper zone 12 adjacent to upper perforations 13 and will not pass below the plug 100.
Although FIG. 1A shows the pressure isolation plug 100 used in a vertical section of wellbore 10, wellbores may also have horizontal sections. Unfortunately, moving completion equipment, such as perforating guns, setting tool, and plugs, in a horizontal section of a wellbore can prove difficult for operators. For example, if a plug is to be used to isolate a bottom zone of a wellbore having a horizontal section, then perforating guns and other equipment must be moved downhole through the horizontal section using a tractor or coil tubing. As one skilled in the art will appreciate, the use of tractors or coil tubing in horizontal applications can be very time consuming and expensive.
Accordingly, a need exists for a pressure isolation plug that can be advantageously used in wellbores having not only vertical sections but also horizontal sections and that can allow perforating guns and other equipment to be moved downhole without the need of tractors or coil tubing. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.